The mechanism of intramembrane electron transfer and structure-function relationships in the energy-transducing cytochrome beta complexes will be studied. The long-term objectives of this study are a deeper understanding of physico-chemical mechanisms governing charge transfer reactions in bioenergetics and development of an improved approach to prediction of structures of membrane proteins and their complexes: structure predicted on the basis of experimental biochemical, spectroscopic, and kinetic data, and molecular modeling will be tested by theoretical evaluation of thermodynamic and kinetic parameters. Studies already carried out provide an explanation for the anomalous positive midpoint oxidation-reduction potential (Em) of the thylakoid cytochrome beta-559 in terms of (i) the Bornian solvation energy of the heme, (ii) the positive dipole potential near the N-termini of the two coordinating trans-membrane alpha-helices, in the context of a three phase model of the membrane. The novel third phase is a proteinaceous surface layer of intermediate dielectric constant that creates a hydrophobic niche for the heme and protects it from water. Similar considerations imply that the measured Em values of the two hemes of cyt beta of the cytochrome beta6 and betac1 complexes can only be explained if the dielectric environment of the hemes is asymmetric, more polar on the electrochemically positive side. It is proposed to (i) examine the correlation between the integrity of the surface layer and the high Em state of the heme; (ii) calculate the Em of cytochromes of known structure, and the kinetics of interheme transfer between the two hemes of the thylakoid cytochrome beta6; (iii) examine the molecular and electrostatic basis for the asymmetric dielectric environment of the two hemes of cyt beta6; (iv) rigorously determine the reference (aqueous) potential of protoheme; (v) determine the factors that control the rate of in situ interheme electron transfer of cyt beta6; and (vi) undertake a spectroscopic study of reorganization energy in electron transport proteins.